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  1. #1
    I'm Done
    Reputation: Durga's Avatar
    Join Date
    Feb 2005

    Using Aluminum or Ti Crank Bolts?

    I have two bikes (both with square taper BB's that use M8 bolts), and I have one set of Ti crank bolts, and one set of alloy that I'm considering using.

    I've been searching for some good info on how to use these bolts responsibly, but I haven't found any concrete advice.

    I know that a steel bolt should be used first and torqued to spec, but how about the lighter bolts? My search has yielded torque recommendations (for alloy) ranging from ~20-88 in/lbs. One report of alum bolts shearing at 25 in/lbs.

    Does anyone have some really good advice on how to use both of these types of crank bolts responsibly?

  2. #2
    mtbr member
    Join Date
    Jul 2010
    When you torque the bolts down it is forcing the crank arm onto the spindle with a press fit. Once the arm is on, the bolt doesn't do much other than keeping the arm tight against the taper so it doesn't work loose. So, once you torque down the steel bolts and remove them you can replace the bolts with the ti or aluminum and tighten them down snug, but no need to overdo it. I'm not sure what the actual torque spec would be. I prefer ti bolts though because you don't have to be as careful with them as far as rounding them off or stripping them.

  3. #3
    mtbr member
    Reputation: loggerhead's Avatar
    Join Date
    Mar 2009
    Yeah, crank em' down good with the steel and put in the alu. after. Not too tight and make sure you spin the socket straight so you don't snap it. I don't use a torque wrench. I just make sure it is snug. I also re-tighten them before every ride as they do usually come a little loose in the rocky trails I ride.

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